Th17-associated cells and signaling pathways are clearly important in the development of multiple autoimmune processes, including rheumatoid arthritis, multiple sclerosis, and psoriasis. IL23 is a prototypical driver of Th17-mediated inflammation, and we and others have shown that repeated injections of recombinant IL23 in mouse skin result in a psoriasiform dermatitis that mimics many of the features of human psoriasis in as little as 5 days. Among the ~20 known chemokine receptors, CC chemokine receptor-6 (CCR6) is particularly important for Th17-directed immune activity since it is both a marker for T cells that express the Th17 phenotype and a critical participant in several mouse models of autoimmune disease, including autoimmune encephalitis, collagen-induced arthritis, and psoriasis. We have previously shown that CCR6-deficient mice fail to develop psoriasiform dermatitis in skin following IL23 injection. Current models suggest that IL23 produced by dendritic cells (DCs) act to sustain dermal CC chemokine receptor-6 (CCR6)-expressing Th17 cells which then produce IL22 as a major downstream effector that stimulates epidermal hyperplasia through STAT3- mediated mechanisms in human skin. Positive feedback is provided by epidermal and dermal production of CCL20, the CCR6 ligand, potentially recruiting more CCR6+ T cells or CCR6+ antigen-presenting cells into inflamed psoriatic skin. While data from human studies are just beginning to implicate ??T cells in psoriasis and other autoimmune disease, our published data demonstrate that a novel population of CCR6+, V?3- T cell receptor (TCR) ?? low (GDL) T cells, distinct from resident dendritic epidermal ?? T cells (DETC), accumulates in murine epidermis following exposure to IL23 and is a major producer of IL22 and IL17 in murine epidermis. We hypothesize that 1) CCR6+ GDL T cells in skin may be critical innate immune cells for the delivery of IL22 and other cytokines that regulate epidermal hyperplasia and inflammation in skin in conditions such as psoriasis and 2) that antagonists of CCR6 or CCL20 would be effective therapeutic agents in several Th17- mediated autoimmune processes, including psoriasis, because of their effects on the trafficking and/or function of CCR6-expressing cells. Based on this hypothesis, we seek to better define the roles of CCR6 and ?? T cells in an IL23- and imiquimod-induced models of psoriasisform dermatitis in mice and to use novel computational methods to identify small molecule lead compounds that antagonize the function of either CCR6 or its ligand, CCL20. Our results will be validated with a SCID-hu psoriasis skin xenotransplant model.